<template>
  <ul class="list">
    <li class="item" v-for="item of letters" :key="item" :ref="item"
    @click="handleLetterClick" @touchstart.prevent="handleTouchStart"
    @touchmove="handleTouchMove" @touchend="handleTouchEnd">{{item}}</li>
  </ul>
</template>

<script>
export default {
  name: 'CityAlphabet',
  data() {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  props: {
    cities: Object
  },
  methods: {
    handleLetterClick (e) {
      this.$emit('change',e.target.innerText)
    },
    handleTouchStart () {
      this.touchStatus = true
    },
    handleTouchMove (e) {
      if (this.touchStatus) {
        if(this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY)/20)
          if(index >= 0 && index < this.letters.length){
            this.$emit('change',this.letters[index])
          }
        })
      }
    },
    handleTouchEnd () {
      this.touchStatus = false
    }
  }
}
</script>

<style lang="stylus" scoped>
  @import '~styles/varibles.styl'
    .list
      display: flex
      flex-direction: column
      justify-content: center
      position:absolute
      top: 1.58rem
      right: 0
      bottom: 0
      width: .4rem
      .item
        line-height: .4rem
        text-align:center
        color: $bgColor

</style>
